The invention relates to an apparatus on a flat card or roller card for textile fibres such as cotton, synthetic fibres or the like, in which a covering comprising work and cover elements lies opposite the clothing of a high-speed cylinder. In one known apparatus—viewed in the direction of rotation of the cylinder—in succession there is an opening for the exit of air (exhaust airflow) and an opening for entry of air (supply airflow), past which openings a flow of fibres and air is passed, wherein, in relation to the cylinder, the spacing of the covering upstream of the exhaust air opening and the spacing of the covering downstream of the exhaust air opening are different.
In EP 0 848 091 A1, a casing part with a deflector, an exhaust air opening (separation gap), a knife with a separating edge, a guide surface and a supply air opening (air inlet in the form of a slot) lie opposite the clothing of the cylinder, viewed in the direction of rotation. The deflector is arranged upstream of the separation slot and together with the cylinder clothing defines a work slot, through which the flow of fibres and air passes. The separating edge of the knife and the guide surface, which are arranged downstream of the separation gap, have very narrow spacings from the cylinder clothing. The closely set edge determines the proportion of the flow of fibres and air that is separated off by the knife, diverted into the separation gap together with the waste (trash) and consequently removed from the work gap (exhaust airflow). Downstream of the edge, a negative pressure and turbulence therefore develop, and are counterbalanced by the supply airflow. The guide surface downstream of the edge is, like the edge, also set so close to the cylinder that no substantial spread of the airflow after the edge is possible. On the contrary, the introduced air flows off substantially in the transport direction. The drawback is that a considerable portion of such fibres, which are supposed to remain in the processing process, commonly known as good fibres, are separated out together with the trash. What is more, an unacceptable proportion of short fibres remains in the layer of fibres on the cylinder. This leads all in all to unsatisfactory cleaning results, which gives rise to adverse effects in yarn production and to loss of yarn quality.